New Region of Hippocampus Essential to Social Memory

Researchers from Columbia University Medical Center (CUMC) have found that a small region of the hippocampus is primarily responsible for social memory. Also known as the CA2, they discovered that it proved to be useful in understanding disorders characterized by social behavior, including bipolar disorder, autism and schizophrenia.

As scientists have long understood the role of the hippocampus in the ability to remember the who, what, where and when for our day to day lives, recent studies have shown that various subregions of the area carry different functions. 

"However, the role of CA2, a relatively small region of the hippocampus sandwiched between CA3 and CA1, has remained largely unknown," said senior author Steven A. Siegelbaum, PhD, professor of neuroscience and pharmacology, chair of the Department of Neuroscience, a member of the Mortimer B. Zuckerman Mind Brain Behavior Institute and Kavli Institute for Brain Science, and a Howard Hughes Medical Institute Investigator, via a press release. 

To study the brain area more, researchers created a transgenic mouse in which CA2 neurons are selectively inhibited by adult animals. As neurons were inhibited, the mice were given

"The mice looked quite normal until we looked at social memory," said first author Frederick L. Hitti, an MD-PhD student in Dr. Siegelbaum's laboratory, who developed the transgenic mouse, via the release. "Normally, mice are naturally curious about a mouse they've never met; they spend more time investigating an unfamiliar mouse than a familiar one. In our experiment, however, mice with an inactivated CA2 region showed no preference for a novel mouse versus a previously encountered mouse, indicating a lack of social memory."

The study findings are discussed further, courtesy of the release: "In two separate novel-object recognition tests, the CA2-deficient mice showed a normal preference for an object they had not previously encountered, showing that the mice did not have a global lack of interest in novelty. In another experiment, the researchers tested whether the animals' inability to form social memories might have to do with deficits in olfaction (sense of smell), which is crucial for normal social interaction. However, the mice showed no loss in ability to discriminate social or non-social odors.

"In humans, the importance of the hippocampus for social memory was famously illustrated by the case of Henry Molaison, who had much of his hippocampus removed by surgeons in 1953 in an attempt to cure severe epilepsy. Molaison (often referred to as HM in the scientific literature) was subsequently unable to form new memories of people. Scientists have observed that lesions limited to the hippocampus also impair social memory in both rodents and humans."

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More information regarding the study can be found via the journal Nature.